1. Field of the Invention
The invention relates to a coupling tooth formation, in particular in a gear box, either on a gear sleeve or on a gear wheel, the teeth of which are positioned at a cylindrical base in relation to the rotational axis, elongate in axial direction and provided at their coupling end with a roof contour sloping from the tooth base towards the tooth head, comprising a rounded roof edge.
2. Description of Related Art
Gear sleeves are known (DE 19604386 A1, DE 19531155 A1) the teeth of which comprise roof-shaped surfaces which together form a rounded edge. Furthermore, symmetrical and asymmetrical roof configurations are known and those having a sloping roof contour; the latter serves to additionally facilitate tracking of the two teeth partners of a set of coupling teeth. In this context it is the object of the person skilled in the art to attain that during the initial contact of the two tooth formations their contact is reduced to a minimum of points or lines; this permits the friction-reduced and, therefore, smooth-running interlocking of both tooth formation partners of a set of coupling teeth. However, in this process still too little attention is paid to the further procedure of the tracking process, that is to say, after the initial contact has already taken place. This is where the present invention sets in by pursuing the object of realizing the smoothest possible transition in the phase between the initial contact and the final coupling position.
This object is attained according to the invention in that the radius of the roof edge rounding increases from the tooth base towards the tooth head according to a pre-set function.
This measure results in a continuous increase of the contact points or the extension of the contact lines until finally the desired surface contact is attained between the power transmitting tooth flanges. During the initial contact, i.e. in the proximity of the foot region with a correspondingly greater tooth depth, the tooth formation offers a particularly great tolerance for the mutual engagement as the radius of the roof edge rounding is relatively small there. With an increasing engagement, i.e. increasing axial shifting of the two interlocking teeth, an increasing centering of the two teeth formations in relation to one another is brought about according to the widening of the roof edge in the tooth head region due to the relatively larger radii there of the roof edge rounding, until their maximum contact is realized upon reaching complete engagement.
In the process, the person operating the gear box, gets the impression of a smoother gear changing procedure as if, after the initial contact, the switched gear is put in quasi automatically. This impression is further strengthened if the increase in radius proceeds progressively, e.g. according to an exponential function or a circular function instead of a linear function.
A particularly advantageous progression from the foot cylinder towards the head cylinder of the tooth formation defines an altogether six-fold increase of the radius in which context doubling is only reached at about 60% of the relative tooth height.
As regards the configuration of a short tooth formation of this kind as a whole, one could, in a graphic transposition of the rules according to the invention, compare the roof shape, in the case of a symmetrical tooth, with a human nose which, at the base of the nose, corresponding comparatively to the foot cylinder of the tooth formation, is designed particularly narrow, subsequently becoming broader up to the tip of the nose. The bridge of the nose may in this context slope either rectilinearly or by being bent downwardly, the lowest point of the nose, by way of comparison, corresponding to the head cylinder of the tooth formation. In order to remain with the demonstrated image, the longitudinal body axis of the nose carrier would correspond to the rotational axis of the tooth formation.
As regards the oblique roof surfaces laterally adjoining the roof edge, these are preferably designed as level planes. This facilitates their shaping in a deformation process. e.g. for the manufacture as a forged part, in which context one or more calibrating steps may follow onto a forging step.
Arched roof surfaces are, however, likewise conceivable within the scope of the invention, but their precise manufacture encounters difficulties with regard to minimum deformations as in the case of coupling teeth. This applies similarly to asymmetrical roof shapes, the manufacture of which presupposes likewise a high precision of the forming tools or of the deformation process.